Roof-rafter-calculating device.



D ROBERTSON & J. A. ATKINSON.

ROOF RAFTER CALCULATING DEVICE. APPLICATION FILED MAY 22; 1911.

Patented May 28 MM mw% M N lpnn m Z f WI TNESTSES:

m ATTORNEY COLUMBIA PLANOGRAPII c0., WASHINGTON. n. c.

' UNITED STATES PATENT OFFICE.

DONALD ROBERTSON AND J MES A. ATKINSON," on NEW WESTMINSTER, RRITIsH COLUMBIA; CANADA.

ROOF-RAFTERTCALCULATING DEVICE.

Specification of Letters Patent.

Application filed May 22, 1911. Serial No. 628,731.

To all whom it may concern:

This invention relates to devices for calcusimplify the construction of the apparatus and render the work performed therewith more readily accomplished.

The invention is illustrated in the accompanylng drawlngs, 1n wh1ch Figure 1 is a plan view of our improved calculator. Fig. 2 is an elevation viewed from the lower edge of Fig. 1. Fig. 8 is a detail section through AA of Fig. 1. Fig.

' 4; is.a plan view illustrating the manner of marking a scantling for bevel-cuts from data derived from the calculator. Fig. 5 is a perspective view of a portion of the roof structure of a house.

According to the present invention, we provide a frame comprising a base member 1 having an arm 2 pivotally connected to its right hand end by a pin 7, and another arm 3 which is pivotally connected by a pin 8 to the free end of the arm 2 and is adjustably secured to the left-hand end of said base-member by a clamping wedge 4 co6perating with a stud 9 fixedly secured to such base-member. The wedge 4 is operatively connected to said base-member by a headed pin 10 passing through a slot 11 in the wedge. A groove 12, desirably of a clovetail shape in cross section, extends longitudinally of the base member for the accommodation of a bar 13.

Slidably connected to the base-member is a blade 5 which is secured in selected positions lengthwise of the base member by a clamping wedge 6 acting against one edge of the base member and in opposition to a bar 14 juxtaposed with the other edge thereof.

icured, as by rivets, to the blade 5 and is extended beyond the lower edge of the blade to carry a pin 16 whereby the wedge 6 is adjustably connected with the blade. Provided upon the blade are spaced marksl? which are designated by numerals, as 17 Patented May 28,1912.

, to indi-- cate distances by scale from a line projected at righta-ngles to the blade and extending through the axis of pivot 7. The arm 2 is likewise provided with gradu ations 18 and indicating numbers, as 18, therefor to denote by scale distances from the axis of the pivot 7.

The slidable bar 13 is also provided with spaced marks 19 with indicating numerals 19 therefor and to a similar scale with the marks on the arm 2 and the blade 5. On the base-member 1 is an index mark X which is located'to coincide with a predetermined mark, as 21, upon the bar when the initial or zero mark of the latter is in alinement with the axis of the pivot 7. A scale 22 is provided on the arm 3 and is graduated to indicate, with reference to an index mark Y on the stud 9, the positions into which the arm 3 is to be adjusted to cause the arm 2 to be presented in appropriate angular positions with relation to the base-member 1 in the operation of the, invention. p

In Fig. 5 is represented a portion of the roof-frame of a building, comprising a ridge board A, a hip rafter B, main rafters G extending from the plate D to the ridge board A, and jack rafters E extending from said plate to the hip rafter.

The manner of employing the invention may be explained as follows: With the rod 13 located as shown in Fig. 1, the blade 5 is first moved into a position, as indicated by scale on rod 18, equal to one-half the width of the building; whereupon the'arm 2 is swung into a position whereat the measuring edge thereof will cross the corresponding edgerof the blade 5 at a point on the lat -ter, according to the scale, equal to the rise or elevation of the ridge board A (Fig. 5) above the plate D. The arm 2 is now secured through the medium of the arm 3 and the wedge 4, and the blade 5 is then i sition whereat the arm 2 crosses the blade 5 it is found, for example, to be located at the graduation mark 8 of the blade scale,

thus affording the rates of the rise to the half-span and which, in this instance, is as eight is to twelve. Employing the factor eight, the arms 2 and 3 are adjusted to present the graduation mark 8 of the scale 22 into register with the index mark Y therefor. The apparatus is thus adjusted and the measurements of the various rafters can be determined therefrom as follows: Supposing one-half the span of the roof to be twelve feet, to correspond with the posi tioning of the parts of the apparatus as illustrated in Fig. 1, the main rafters C will be found by the scale .on the blade where the latter intersects the arm 2' to be fourteen and four-tenths feet, while the scale on the arm 2 indicates that the length of a hip-rafter B is eighteen and eight-tenths feet, and to which lengths the respective rafters may be out. By successively shifting the blade 5 toward the pivot 7 to distances equal to the spacing of the jack rafters E, as denoted by the scale on the bar 13, the lengths of such jack rafters are found from the intersection of the blade 5 with the arm 2 and read from the blade scale. The lengths of the rafters are laid off to their true measurements by rule on appropriate scantlings for roof timbers. The bevels at which the ends of a main-rafter B (Fig. 4:) are to be out, are found by laying a carpenters square S so that the squaretongue S will have the inch mark eight thereon at the intersection of one of the end marks previously made with the scantling edge B and the twelve-inch mark of the square-stock S" coincide with the same edge R of the scantling. A scratch or pencil mark is then made upon the scantling along the edge M of the square stock S to inclicate the proper cutting line for the heel of a mainrafter. The top or ridge cut is similarly found except that the cutting line is made along the edge M of the square tongue when the same is held against the other of the length marks. The jack rafters E are similarly marked by the square to lengths ascertained from the blade scale at the intersection of the blade 5 and arm 2 when the former is successively shifted distances equal to the spacing of these rafters; as, for

example, sixteen inches. The marks for a out upon a hip rafter B are obtained by employing in the same manner the designating mark of the scale on arm 2, as will be understood. The purpose of having the bar 13 slidable is to permit the same to be shifted a distance equal, by scale, to the amount of the overhang of the various rafters, and when thus set the lengths of the rafters may be determined, as above explained, without regard to the increment due to such overhang of the rafters.

WVhat we claim as our invention, is-

1. In aninstrument of the character de scribed, a base-member, a bar provided with a scale and slidable longitudinally in said base member, an arm hingedly connected at one of its ends to an end of said base mem ber, a second arm hingedly connected with the free end of the aforesaid arm, scales provided on-the respective arms, means for securing the free end of the second named arm with the end of said base-member remote from the connection of the latter with the first named arm, a blade provided with a scale and shiftable lengthwise of the base member, and means for securing said blade to the base member in various adjusted positions and at right angles to such member.

2. In an instrument of the class described, a base member, a bar shiftable longitudi nally therein and provided with a scale, a blade provided with a scale and slidably connected to said member, means for securing said blade in adjusted positions, an arm hingedly connected at one end to one end of said member and provided with a scale, an-

other arm hingedly connected at one end to the free end of the aforesaid arm and provided with a scale for indicating the inclination of the first named arm from said member in terms of the ratio of the rise of a roof to half its span, and means for securing said second named arm to the base member at various adjusted posit-ions.

DONALD ROBERTSON. J AMES A. ATKINSON.

Witnesses HORACE BARNES, E. PETERSON.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

